This invention relates to a novel structure of an alumina body having a conductive coating thereon. More particularly, it relates to an alumina body having a conductive coat suitable for making e.g. a pickup stylus for the video disc playback system of a capacitance variation type.
Alumina such as sapphire or ruby the main constituent of which is .alpha.-Al.sub.2 O.sub.3, and which has a conductive coating thereon is widely used to make, for instance, a pickup stylus for a video disc playback system of the capacitance variation type or a variable resistor having a thin metal film coating for use in an electrical circuit. The conductive coating, however, is not very adhesive with respect to the alumina because of the high chemical stability of the surface of the alumina. Several attempts have been made to increase the adhesive force of the conductive coat with respect to the alumina. For instance an irregular surfacehas been provided on the alumina to increase the adhesion of the conductive coating to the alumina surface. These aluminas, however, have shortcomings such as the non-uniformity of the cnductive surface coating.